Recently, there are a wide variety of types of optical devices, and many of them have a structure in which an antireflective, low-refractive index film is formed on the surface of an optical instrument. The optical instrument is not limited to devices having flat surface morphologies, and includes brightness enhancing lenses and diffusion lenses in the backlights for liquid crystal displays, Fresnel lenses and lenticular lenses used in screens of video projection televisions, microlenses, and the like. In such the devices, desired geometric-optical performance is obtained as a resin material mainly forms a microstructure. Thus, in order to impart an antireflection property, it is necessary to form a low refractive index film in an appropriate form on the surface of such a microstructure body.
Research and development has been hitherto achieved on a material for forming the low refractive index film. For example, it has been suggested to use a polysiloxane that is obtained by condensing a silane compound having a radical polymerizable organic group, a silane compound having a fluorine atom, and an alkoxysilane compound (see Patent Literature 1 and the like). It is reported that the unevenness of a coating film in the vicinity of the wall portion of the structure can be improved thereby.